The disclosures of Japanese Application No. 11-20323 is hereby incorporated by reference.
1. Field of the Invention
This invention relates to a thermochromic dry offset ink, and a printed article produced using the ink. More particularly, it relates to a thermochromic dry offset ink which, in the steps of printing and heat curing, satisfies pressure resistance and heat-resisting strength and imparts ink transfer performance and uniform printing effect.
2. Related Background Art
The present applicant has proposed a thermochromic dry offset ink making use of a thermochromic pigment material or composition prepared by making into microcapsules a reversible thermochromic material containing three essential components consisting of an electron-donating color-developing organic compound, an electron-accepting compound capable of making the electron-donating color-developing organic compound develop a color and a reaction medium capable of controlling the temperature at which the color-developing reaction of the both compounds takes place (Japanese Patent Application Laid-Open No. 8-277373).
The above proposal intends to improve roll-to-roll ink transfer performance to achieve improvements in uniform printability and high-speed continuous printability in dry offset inks making use of thermochromic pigment materials.
The present inventor has made further researches on the above thermochromic dry offset ink. Accordingly, an object of the present invention is to provide a thermochromic dry offset ink which can more improve pressure resistance and heat resistance and also can more satisfy uniform printability and high-speed continuous printability, and a printed article provided with a thermochromic print layer formed using such an ink.
To achieve the above object, the present invention provides a thermochromic dry offset ink comprising a dry offset ink medium and a thermochromic pigment material dispersed therein, wherein the thermochromic pigment material is a pigment material which has a microcapsular form having non-round particle cross section and has a thermochromic material enclosed in the microcapsules.
As a preferred embodiment of the present invention, the thermochromic pigment material may have an average particle diameter [(length+breadth)/2] of from 1.0 xcexcm to 5.0 xcexcm;
the thermochromic pigment material may be a pigment material which has a microcapsular form of thermochromic material/wall film=7/1 to 1/1 (weight ratio);
the thermochromic pigment material may be a pigment material having a hollow at some part of a particle outer surface;
the thermochromic dry offset ink may contain at least one fine powder having the function of a spacer, selected from a fine thermosetting-resin powder, a fine thermoplastic-resin powder and a fine inorganic-material powder which have particle diameter larger than the average particle diameter of the thermochromic pigment material; the fine powder being mixed in an amount ranging from 5% by weight to 20% by weight; or
the thermochromic pigment material may be held by from 10 parts by weight to 60 parts by weight per solid matter of the medium, based on 100 parts by weight of the medium.
The present invention also provides a printed article provided with a thermochromic print layer formed by offset printing, in which layer a thermochromic pigment material which has a microcapsular form having non-round particle cross section is fixed standing dispersed in the medium.